It has been a goal in wireless communications to devise a mechanism to enable a wireless transmit/receive unit (WTRU) to place or receive a communication during an ongoing session without service interruption. For example, in a Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) scenario, a goal has been to devise a mechanism to enable a WTRU, while it is connected to a packet switched (PS) domain of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), to place (i.e., originating) or receive (i.e., terminating) circuit switched (CS) services or vice versa. Examples of CS services may include at least such services as a CS voice call, a short message service (SMS), location services, or supplementary services.
In some wireless communication deployment scenarios, some services may initially be provided by a particular Radio Access Technology (RAT), in which case the WTRU may be required to perform a handover to a target RAT prior to canceling an initiated service. Performing a handover may lead to service interruption at the source RAT. In systems such as Global System for Mobile communication (GSM), Universal Mobile Telecommunications System (UMTS), or Code Division Multiple Access (CDMA), a user may cancel an ongoing mobile originated (MO) session request before the session setup is completed. For example, in a GSM deployment scenario, a connection management (CM) entity may handle session cancellation procedures. In this example, if a user decides to cancel an initiated session before the session setup is completed, the CM entity may send a cancel message. A handover to the target RAT, however, may be performed in order to cancel the initiated session.
In an LTE example, a WTRU may perform a CS fallback (CSFB) procedure to initiate a CS session during an ongoing PS session. Because a CS session request via LTE may force the WTRU to change RATs, canceling a CS session request when the WTRU is camped on an LTE cell may cause numerous problems.
For example, depending on the time at which the user cancels the ongoing CSFB procedure, signaling messages may have been exchanged or may be in the process of being exchanged between network entities in preparation to execute the CSFB. This may lead to problems such as service interruption, time delay, or unnecessary resource drain. For example, the source and target network nodes may exchange signaling messages to prepare resources for the terminal. Not expecting the WTRU to cancel the request, the mobility management entity (MME) may begin performing actions to complete the procedure by forwarding user context information to the target RAT to which the WTRU will handover. If the WTRU has an ongoing PS session in LTE, the MME may transfer the required context to the target RAT so that resources may be reserved to handoff the PS session. It would therefore be desirable to have a method and apparatus to address WTRU behavior when a session request is canceled before session setup is completed.